> PHOTOSHOP USER>^ FEBRUARY 2020[ 120 ]
ANSWERS TO PHOTOSHOP AND GEAR-RELATED QUESTIONS
When we use the word “resolution” in the context of Photo
shop, it can refer to several different concepts:- Image resolution is the size of the image’s pixels
when printed. - Camera resolution is the specific number of pixels
captured by your camera. - Monitor resolution is the number of pixels displayed
on your screen. - Printer resolution does not refer to pixels, but rather
the number of ink droplets required to reproduce
each image pixel on paper or other substrate. It
takes quite a few ink droplets to reproduce each
image pixel, so a printer’s “resolution” number
will be huge compared to an image’s resolution.
(Remember that each pixel in a typical RGB image
can be any one of millions of colors, and your
printer only uses a limited number of inks, so it
takes lots of very tiny droplets to make your eye
see the pixels’ individual colors.)
In this column, we’ll look primarily at image resolution.
The first thing you need to wrap your head around is that
“image resolution” refers only to the physical output of
an image, whether it be via an inkjet printer, laser printer,
imagesetter, blueprint plotter, or other device. “Image
resolution” does not refer to how your image appears on
your monitor or screen. It does not refer to how an image
appears on a webpage. It does not determine how your
image appears in Photoshop.
“Wait, what? Has Pete finally cracked? Of course I need
to consider image resolution when preparing photos and
graphics for my website! Each image must be 72 pixels per
inch (ppi) for a Mac and 96 ppi for a Windows computer!”
In a word: “Not!” (Okay, we’ll let a professional make
a decision about that “cracked” comment, but I’ll explain
the rest.) A photo that measures 1024 x768 pixels appears
exactly the same onscreen in Photoshop and on another
person’s screen when visiting your website, regardless of
resolution. A photo measuring 1024 x768 pixels at 72 ppi
is 786,432 pixels in total; 1024x768 pixels at 300 ppi is
also 786,432 pixels. Your monitor and the screens display
ing your website show only a certain number of pixels, and
those pixels are the same size, regardless of the image reso
lution embedded in the file’s metadata.
Let’s now take a closer look at that phrase “pixels per
inch.” That refers to how many image pixels will be printed
along each inch of paper (or other substrate). At 300 ppi,
each image pixel is printed at a size of 1/300" square. At
72 ppi (not a typical print resolution), each pixel would be
printed as a square measuring 1/72" square. (Note: Images
can also use resolution measured in pixels per centimeter,
abbreviated ppcm.)
The “squareness” of a pixel comes into play primar
ily with images at lower resolutions (smaller ppi values).
Because each pixel is printed as a larger square, some fine
detail in the image can be lost. In addition, those printed
squares line up in a “raster,” a square or rectangle with each
pixel perfectly aligned with those above/below and left/right.
Curves and angled lines can look choppy or jagged at lower
print resolutions. This aspect of resolution, as well as the
exceptional status of vector type, may be explored in more
detail in a future column. nIn a recent issue of Photoshop User you discussed the importance of image resolution and pixels per
inch. Can you please elaborate?—QuinnPETERBAUER
From the Help Desk